[1] Chongqing Univ, Coll Math & Stat, Chongqing 630044, Peoples R China
[2] Univ Calif Davis, Dept Stat, Davis, CA 95616 USA
[3] Beijing Univ Technol, Sch Math & Appl Phys, Beijing, Peoples R China
[4] Hong Kong Baptist Univ, Dept Math, Kowloon Tong, Hong Kong, Peoples R China